Mozilla's next update for Firefox, due tomorrow, will be the first browser to regularly check for outdated third-party add-ons.

Firefox 3.6 will check for outdated versions of Flash Player, and other out-of-datevulnerable plug-ins from vendors like Apple, Adobe, Microsoft and Sun, said Mozilla.

One security expert applauded the news. "This is a great way of improving the security of Web browsers," said Wolfgang Kandek, chief technology officer at security firm Qualys, in a blog entry Saturday. "Flash is often used by attackers to exploit client machines and unfortunately notoriously difficult to update, requiring, on Windows, different update packages for Internet Explorer and all other browsers."

Firefox 3.5.3 and Firefox 3.0.14, security updates for the newest Firefox 3.5 and 2008's Firefox 3.0, respectively, are set to release Sept. 8. After installing either of those two updates, Firefox users will see a message if their computer has an out-of-date version of Flash Player. "You should update Adobe Flash right now," the message will read. "Firefox is up to date, but your current version of Flash can cause security and stability issues. Please install the free update as soon as possible."

The message will also include a link to the download site for the latest Flash Player plug-in.

"For now, our focus is on the Adobe Flash Player both because of its popularity and because some studies have shown that as many as 80% of users currently have an out-of-date version," said Johnathan Nightingale of the Firefox security team, in an entry to the group's blog.

Nightingale was referring to a mid-August report by New York City-based security company Trusteer, which said that two weeks after Adobe patched Flash , almost 80% of the 2.5 million PCs scanned by Trusteer's security service had not yet been updated.

Some of the users most immediately affected by Firefox's new plug-in check will be those running Apple's new Snow Leopard operating system. Apple shipped a months'-old copy of Flash with Snow Leopard, and even "downgraded" current versions during the upgrade to a vulnerable edition of Flash.

Starting Tuesday, Firefox users running Snow Leopard will be alerted to that fact after they update their browsers. More reading: